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Re: Question for Dr. Grewal

  • Subject: Re: Question for Dr. Grewal
  • From: Parwinder Grewal <grewal.4@osu.edu>
  • Date: Thu, 10 Jan 2002 09:13:06 -0500

Bill,

You have made some excellent observations on the exposure of nematode 
infected hostas to the sun.  I have made similar observations also.  In 
fact there are two factors, temperature and ultraviolet (UV) radiation that 
affect nematodes.  Nematodes are very sensitive to ultra violet 
radiation.  In our tests with UV light emitted from a lamp in the 
laboratory, most nematodes were killed in the leaves with just one hour 
exposure.  Thus putting nematode infected hosta plants in the sun (exposed 
areas) is likely to reduce nematode infection.  If most leaves are exposed, 
it could actually cure the plants of nematode infection.  We are doing such 
experiments.

Yes, temperature could be important as well, but hot temperatures may also 
kill the plant, so I would not recommend to place plants in closed 
cars.  Exposure of plants to the sun on driveways for a few days is a good 
idea.

Yes, the nematodes have the ability to move up and down the plant, but you 
are also right that successful reproduction occurs only under favorable 
temperature and minimal UV light.

Yes, different stages of nematode life cycle show differences in tolerance 
to temperature and nematicides.  Eggs are most tolerant.  Nematodes in the 
dry leaves can enter into what we call anyhydrobiosis (life without water) 
and then become very tolerant of both the high and low temperatures.  This 
is one of the ways this nemtaode can survive in the dry plant material.

It is possible that animals moving through wet plants can carry nematodes 
and aid in their dispersal in the garden, but I shall not consider them as 
the major source of dissemination.  Perhaps the biggest source would be 
water (rains, floods, and watering).  Treating plants as soon as the 
nematode symptoms become evident is always a good idea.

Keep firing away the good questions.

Parwinder Grewal

At 04:58 PM 01/09/2002 -0500, you wrote:
>        I've noticed that in hostas that receive a lot of direct sunlight,
>nematode damage in the upper, more exposed leaves is rarely seen. If the
>plant is infested the damage shows only on leaves that are shaded by the
>outer leaves. This would indicate that they are sensitive to the
>temperatures that can develop in a leaf that is heated by the sun, and will
>avoid those leaves. It would also seem to indicate that they can move
>through the plant down at the crown level, where the leaves join. Would you
>say this is so? Or are they randomly entering leaves and only reproducing
>successfully where the temps stay cooler? Do you think impromptu treatments
>such as leaving infested plants on a black driveway for a few days in hot
>weather or putting them inside closed cars in same would have much effect?
>Are different stages destroyed at different temperatures?
>         If you're not tired of answering, one more---- What possibility is
>there of nematodes spreading around a garden carried by animals running
>through wet leaves after a rain? This seems a possibility to me if
>populations are high and thriving in one area, and a strong argument for
>treating immediately when you first discover them.
>         Sorry about the endless string of questions, but many hosta
>gardeners still think they are harmless and not worth bothering to treat
>for. I have been breeding hostas and collecting sports for some time now, so
>disposing of plants, especially seedlings, is not a choice.
>
>...........Bill
>
>
>
> > Bill,
> >
> > I replied to a very similar question yesterday.  I hope you got the answer
> > to your question.  The nematodes become active soon after the plants start
> > sprouting. Due possible injury (phytoxicity) to young plants, I would wait
> > spraying until early May.
> >
> > Parwinder
> >
> > At 02:16 PM 01/08/2002 -0500, you wrote:
> > >Another thing most people seem confused about is when in the spring they
> > >become active. Because symptoms do not show in hosta until midsummer, it
>is
> > >impossible to tell without a microscope if a plant or bed is infested.
>This
> > >causes most gardeners to think in terms of beginning control measures at
> > >that time. When do nematodes come out of dormancy in the spring, and when
> > >should treatment begin?
> > >
>.........Bill
> > >Meyer
> > >
> > >
> > > > Yes, the rate of spread is about right and it depends mainly on the
>soil
> > > > type, slope and water.
> > > >
> > > > No nematicide provides 100% control of nematodes, but there are no
>reports
> > > > on the development of resistance in nematodes under field
> > > > conditions.  Furthermore, the mode of action of ZeroTol is such that
> > > > resistance development is not really possible.
> > > >
> > > > Regular applications of ZeroTol to infected plants will reduce spread
>of
> > > > the nematodes in a garden.  Plucking of infected leaves as soon as the
> > > > symptoms of nematode infection become clear followed by a thorough
> > > > clean-out in the fall can substantially reduce nematode spread.
> > > >                 - Parwinder Grewal
> > > >
> > > > At 01:13 PM 01/08/2002 -0500, you wrote:
> > > > >Hi Dr.Grewal,
> > > > >              Thank you for answering. From what I've seen, they seem
>to
> > > > >spread at a rate of about ten feet a year in all directions, more if
> > > > >downhill. Would this seem about right? Your findings indicate that
> > >ZeroTol
> > > > >kills about 80% when plants are in the ground, if I remember right.
>Would
> > > > >this make it likely that a resistant strain would develop? Also would
> > >using
> > > > >ZeroTol regularly control the spread, or would they continue to
>spread
> > > > >through the rest of the garden at more or less the same rate?
> > > > >
> > > > >.........Bill Meyer
> > > > >
> > > > >
> > > > > > Hi Bill,
> > > > > >
> > > > > > I know that most effective nematicides are no more available to
> > >control
> > > > > > foliar nematodes and there are many restrictions the use of other
> > > > > > chemicals.  In our research, we have discovered that ZeroTol,
>which is
> > > > > > currently used as a general sterilant/fungicide, is an effective
> > > > >nematicide
> > > > > > against foliar nematodes.  This chemical can be applied by home
> > > > > > owners.  Our findings on ZeroTol and other chemicals to
> > >control/suppress
> > > > > > foliar nematodes were published in the Spring issue of Hosta
>Journal
> > >in
> > > > > > 2001.  There are also other useful tips and preventive measures
> > >described
> > > > > > in that article.
> > > > > >
> > > > > > Yes, foliar nematodes can eventually kill hosta plants if they are
> > >ignored
> > > > > > for long.  Overtime nematode populations build up on plants and in
>the
> > > > >soil
> > > > > > around plants.
> > > > > >
> > > > > > Parwinder Grewal
> > > > > > Assistant Professor
> > > > > > Department of Entomology
> > > > > > OARDC
> > > > > > The Ohio State University
> > > > > > 1680 Madison Ave
> > > > > > Wooster, Ohio 44691, USA
> > > > > > Phone (330) 263-3963
> > > > > > Fax (330) 263-3686
> > > > > >
> > > > > >
> > > > > > At 11:31 AM 01/08/2002 -0500, you wrote:
> > > > > > >Hi Dr. Grewal,
> > > > > > >           A question that is commonly asked on the lists is what
>can
> > >the
> > > > > > >average gardener who does not have access to restricted chemicals
> > >like
> > > > > > >Nemacur do about foliar nematode infestation. Because of changes
>in
> > >the
> > > > > > >pesticide laws, many of us find ourselves with these pests
>running
> > > > >rampant
> > > > > > >and we are not permitted to use the chemicals that best control
>them.
> > > > >What
> > > > > > >would you say is the most effective treatment we could use?
> > > > > > >           Another somewhat related question is ------What would
>you
> > >say
> > > > >the
> > > > > > >long-term effects on hosta are of untreated or poorly treated
>foliar
> > > > > > >nematode infestations? Can they kill plants eventually?
> > > > > > >
> > > > > > >..........Bill Meyer
>
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